In recent years, a WiFi mounting rate of a personal computer (PC) is extremely high, whereas a cellar system mounting rate of a PC is still low. Therefore, the following service is performed. That is, data communication is first performed via a base station by utilizing a cell phone mounted a cellar system having a high cover rate of a wireless communication area, a PC and the cell phone are connected with each other by utilizing a WiFi communication module (WLAN communication module) or a Bluetooth communication module included in this cell phone. And the cell phone transfers data obtained via the base station to the PC. In this case, a user operates the cell phone to make settings for performing the above-mentioned series of service, whereby the service between the cell phone and the PC is started. Incidentally, WiFi is a name indicating that the connectivity between wireless LAN (WLAN) devices utilizing communication standards of IEEE802.11a or IEEE802.11b is certified by the Wi-Fi Alliance.
Recently, a chip applied a standby power consumption minimizing technology has also been known (see, for example, JP2009-89434A). The chip (hereinafter, referred to as “EcoChip”) is mounted on a cell phone, and then the cell phone is applied to the above-mentioned service, which makes it possible to always monitor a service request (connection request) from a PC by the EcoChip. More specifically, through the application of the EcoChip to the above-mentioned service, the cell phone performs local communication between the PC, so that the WLAN communication module which has large power consumption can be powered off, and the connection request from the PC at the other end can regularly be monitored by the EcoChip having small power consumption. As a result, it is possible to omit, at low power consumption, a user's work of directly operating the cell phone. Here, the EcoChip included in the cell phone judges on the basis of only a reception strength on a time axis whether or not a received signal is an activation request signal for requesting the activation of a WLAN communication module of a cell phone 1 which is utilizable as an AP. In view of this, the EcoChip detects a continuous signal transmitted by a unique transmission series or in a constant period.
Three systems are conceivable as a system in which a PC utilizes a WLAN communication module included in the PC to transmit radio waves. The first transmission system is a system in which the PC changes a mode of the WLAN communication module into an AP mode to transmit a Beacon signal by using the WLAN communication module. The second transmission system is a system in which the PC changes the mode of the WLAN communication module into an Adhoc mode to transmit a Beacon signal by using the WLAN communication module. Further, the third transmission system is a system in which the PC changes the mode of the WLAN communication module into an STA mode (STATION mode) and sets a scanning system in the STA mode to Active Scan to transmit a Probe Request signal by using the WLAN communication module.
However, in a conventional WiFi communication system, a de facto transmission period of a Beacon signal of an AP is 102.4 ms, and hence both a transmission period of the first transmission system and a transmission period of the second transmission system are basically the same as the de facto transmission period of 102.4 ms. Therefore, in the above-mentioned service, it has been difficult for the cell phone which communicates with the PC by using the WLAN communication module to distinguish a normal Beacon signal from the AP and a Beacon signal from the PC.
In addition, a transmission period of the third transmission system is also the de facto transmission period (102.4 ms) of the Beacon signal of the AP in many cases. Therefore, similarly to the first transmission system and the second transmission system, in the above-mentioned service, it has been difficult for the cell phone which communicates with the PC by using the WLAN communication module to distinguish the normal Beacon signal from the AP and the Probe Request signal from the PC.
Further, the PC scans every WiFi channel for each predetermined search period, and for the purpose of electric power saving, the PC remains in a sleep state until the next search is performed and intermittently wakes up for each search period (this series of operations is referred to as “intermittent operation”). Accordingly, for example, in the case where the EcoChip included in the cell phone adopts a detection algorithm which requires a certain number of samples due to a narrow bandpass filter and the like, the number of samples corresponds to the number of WiFi channels (WLAN channels), so that the PC cannot continue to transmit, in a constant period, the number of samples of Probe Request signals which enables detecting the Probe Request signals. Therefore, in the case of the third transmission system, in addition to the difficulty in distinguishing the normal Beacon signal from the AP and the Probe Request signal from the PC, the cell phone which communicates with the PC by using the WLAN communication module cannot secure the number of samples of Probe Request signals, which leads to a subject in reception characteristics of the EcoChip.